Knowledge of various torque values within an automatic transmission is useful for many aspects of powertrain control. For example, knowing the input and output shaft torque of a transmission gear box is particularly useful for controlling the transmission to provide consistent and robust transmission shifts. Using these torque signals along with input and output shaft speeds facilitates accurate estimation of individual clutch torques during a shift. One such control system and method are described in United States patent application publication number US20100318269, filed on 23 Aug. 2010, which is hereby incorporated herein by reference.
For cost or other considerations it is not always possible to directly measure each torque within the transmission, and therefore, control system specialists rely on various transmission models to estimate torque values that are not directly measured. In one such model, a quasi-static nonlinear model of a torque converter within the transmission is used to provide torque estimates. Such models rely on multiple nonlinear functions, and are therefore not readily susceptible to adaptive modeling techniques where the values of the estimates are periodically improved. This is because the estimated value, when it is found to deviate from a verifiable value, may require adjustment of one or more of the nonlinear functions in the model, but it is not possible to know which function or functions requires adjustment. Therefore, a need exists for a system and method for a vehicle transmission that provides accurate and adaptable estimates of transmission torque.